The present invention relates generally to paper handling apparatus and more particularly to a buffer mechanism used in a photofinishing system for conveying a cut sheet from one work station of the system operating at a first speed to a second workstation of the system operating at a faster speed.
In a photo finishing system of the type for which this invention relates, prints as created by an ink jet printer are dried, cut into sheets that may include one or a number of prints, and then the sheets are laminated to protect the images. The lamination process is continuous in that the laminating material is applied to the cut sheets from a continuous roll of donor material. In order to minimize waste of the laminating material, it is desirable that the space between cut sheets be as small as possible. The desire for as small a space as possible between adjacent sheets is balanced against the need to prevent the leading edge of a following sheet from contacting the trailing edge of a leading sheet during the processing of the sheets. Accordingly, while it is necessary to maintain some gap or spacing between the cut sheets, this gap preferably is as small as possible.
The lamination process requires the application of heat and pressure to the sheets to effectively carry out the lamination process. Typically, this is done with lamination rollers that provide both the heat and pressure and this dual function makes the rollers somewhat bulky. The lamination process further requires that these rollers operate at an essentially constant speed and that the rollers operate continuously. It is important that the rollers not stop during the lamination process as this could destroy a sheet of prints.
From the laminator, the sheets may be fed to an embosser to provide the photographs with a desired matte finish. Like the laminator, the embosser uses relatively heavy rollers that carry out the embossing process by producing a textured surface on the laminate. The embosser rollers may be heated and need to operate continuously to produce a satisfactory surface. Also, the embossing process tends to proceed faster than the laminating process so there is a difference in the speed at which the laminating and embossing rollers operate. Thus, the problem exists of delivering the cut sheets from the laminator to an embosser operating at a faster speed.
The cut sheets emerging from the laminator may not be perfectly aligned when they are delivered to the embosser. Passing a skewed laminated sheet through the embosser will adversely effect the quality of the finished print. Accordingly, if the sheets are skewed leaving the laminator, it is necessary to realign or xe2x80x9cdeskewxe2x80x9d the sheets before delivering them to the embosser.
One method for deskewing is to provide a pair of transport rollers positioned to form a nip. If no corrective action is taken, a sheet of paper entering the nip at an angle will engage the rollers first at one point on the leading edge. The paper then will progressively enter the nip along the leading edge until the other side is reached so the sheet will pass through the nip in a skewed orientation. However, if the transport rollers are stopped the leading edge will butt against the nip and will align itself with the nip as the portion of the sheet immediately behind the leading edge forms a buckle or curled portion that takes up the skew. The transport rollers can then be energized to advance the now aligned sheet through the nip.
Stopping the transport rollers for a time sufficient to remove the skew at the leading edge of a first sheet causes the following sheet to close the gap between it and the trailing edge of the first sheet. Accordingly, the transport rollers must operate at a speed higher than a speed at which the cut sheets are delivered from the laminator or the buffer will fall behind, which is not acceptable.
As noted above, the operating speed of the embosser preferably is faster than the operating speed of the laminator. This arrangement allows the embosser to accept sheets from the transport roller without creating a backup. However, with the embossing process and laminating process operating at different speeds, the buffer must be long enough to accommodate the longest sheet being processed so that a sheet does not simultaneously engage the embosser rollers and the lamination rollers.
Accordingly, it is an object of this invention to provide a buffer for receiving cut sheets from a laminator in a photo finishing machine, deskewing the sheets, and delivering the sheets to an embosser.
It is another object of this invention to provide a buffer that accommodates the different operating speeds of the laminator and the embosser and provide an efficient transfer from one to the other while minimizing the gap between sheets.
While this invention is particularly well suited for the purpose just described, it will be understood that the nature of the processes that immediately precede and follow the buffer is not an element of the invention. The buffer can be used between any two processes where the requirements for receiving sheets for one process and delivering them to a second process are similar to those presented by the laminator and embosser described herein.
Briefly stated and in accordance with the presently preferred embodiment of the invention, a buffer of the present invention is disposed between a laminator and an embosser in a photo finishing machine. The buffer includes deskewing rollers forming a nip for receiving a leading edge of a cut sheet in a skewed orientation and registering the edge parallel to the rollers. Drive rollers deliver the cut sheets to the deskewing roller along a guide track at a speed equal to the output speed of the laminator.
A controller, operatively connected to the deskewing rollers and the drive rollers, stops the deskewing rollers to allow the drive rollers to move the leading edge of the cut sheet against the nip and form a slight buckle in the cut sheet. The controller then starts the deskewing rollers to advance the cut sheet partly through the deskewing roller and again stops the deskewing rollers. During all this time the drive rollers continue to feed the cut sheet to the buffer from the laminator. Stopping the deskewing rollers prevents the possibility that the leading edge of the cut sheet will enter the embosser while the trailing edge of the sheet is still in the grip of the laminator or of the drive rollers.
The guide track has a trap that opens on command from the controller so continued operation of the drive rollers forms a service loop of the cut sheet that extends through the open trap. In this fashion the buffer can accommodate a length of cut sheet that is longer than the guide track. A sensor signals the controller upon the passage of the trailing edge of the cut sheet past a fixed point. This indicates that the trailing edge of the cut sheet is free of the laminator. When this happens, the deskewing rollers are activated to turn at a faster speed that matches the operating speed of the embosser. The timing is such that the trailing edge of the cut sheet will clear the drive rollers before the service loop is depleted so the cut sheet is not put into tension by rollers operating at different speeds.
As the trailing edge of the first sheet clears the drive rollers, it drops away from the drive rollers and through the open trap to create vertical clearance between the drive rollers and the trailing edge. Due to the length of the service loop and the speed at which it is drawn by the deskewing rollers, it is possible that the leading edge of the following sheet entering between the drive rollers will overtake the trailing edge of the first sheet. Keeping the trap open and creating the vertical clearance as noted above prevents the leading edge of the following sheet from contacting the trailing edge of the first sheet. The controller keeps the trap open until a gap between the first sheet and the following sheet is reestablished and then the trap is closed so the guide track can direct the leading edge of the following sheet to the deskewing rollers.
Accordingly, the present invention may be characterized in one aspect thereof by a buffer disposed between two workstations. The buffer receives cut sheets from a first work station operating at a first speed and delivers the cut sheets to a second work station operating at a second speed faster than the first speed. The buffer acts to maintain a separation or gap between the trailing edge of a first sheet and a leading edge of a following sheet and comprises:
a) deskewing rollers at the exit defining a nip for receiving a leading edge of a first cut sheet in a skewed orientation and deskewing the leading edge to realign the leading edge parallel to the nip;
b) drive rollers at the inlet end delivering cut sheets to the deskewing rollers at a speed equal to the output speed of the first workstation;
c) a controller operatively connected to the deskewing and drive rollers, the controller being operable to stop the deskewing rollers while continuing activation of the drive rollers to engage a leading edge of a first cut sheet against the nip of the stopped deskewing rollers, form a buckle and deskew the leading edge of the first cut sheet and then activating the deskewing rollers to advance a portion of the first sheet through the nip of the deskewing rollers and then stopping the deskewing rollers all the while continuing the activation of the drive rollers to move the first cut sheet into the buffer at a speed matching the speed of the first work station;
d) a guide defining a path of travel from the drive rollers to the deskewing rollers, the guide accommodating a service loop that is longer than the path of travel, a cut sheet being formed into the service loop by continuing the operation of the drive rollers while the deskewing rollers are stopped;
e) a sensor operable to signal the controller responsive to the passage of a trailing edge of a cut sheet from the first work station;
f) the controller acting responsive to the signal for driving the deskewing rollers at the second faster speed to move a first cut sheet from the buffer and into the second work station at a speed matching the second work station speed; and
g) means creating a vertical separation along the path of travel between the trailing edge of a first cut sheet and a leading edge of a second cut sheet to insure a non contact spacing between the trailing edge of the first sheet and the leading edge of the second sheet as the second cut sheet is moved by the drive rollers into the buffer at the first speed and the first sheet is being moved out of the buffer at the second faster speed.
In another aspect, the invention may be characterized by a method for buffering cut sheets moving from a first workstation operating at a first speed to a second workstation operation at a faster speed, the method comprising:
a) receiving a leading edge of a first cut sheet at a nip between stationary deskewing rollers to deskew the leading edge and form a buckle in the cut sheet adjacent the deskewing rollers;
b) advancing the first cut sheet partly through the nip and then stopping the deskewing rollers;
c) forming a service loop in the first cut sheet;
d) drawing the first cut sheet including the service loop completely through the deskewing rollers while advancing a leading edge of a second cut sheet to the deskewing rollers; and
e) creating a vertical separation between the trailing edge of the first cut sheet and the leading edge of the second cut sheet to insure a non contact spacing between the trailing edge of the first sheet moving through the deskewing rollers and out of the buffer and the leading edge of a second sheet moving into the buffer and towards the deskewing rollers.